<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>姓名案例_watch实现</title>
  <!-- 引入Vue -->
  <script type="text/javascript" src="../js/vue.js"></script>
</head>

<body>
  <!-- 准备好一个容器 -->
  <div id="root">
    姓: <input type="text" v-model="firstName"> <br /><br />
    名: <input type="text" v-model="lastName"><br /> <br />
    全名: <span>{{fullName}}</span>
  </div>
</body>

<script type="text/javascript">

  new Vue({
    el: '#root',
    data: {
      firstName: '张',
      lastName: '三',
      fullName: '张-三'
    },
    watch: {
      firstName(val) {
        this.fullName = val + '-' + this.lastName
      },
      lastName(val) {
        this.fullName = this.firstName + '-' + val
      }
    }
  })
</script>

</html>